a. Field of the Invention PA1 B. Description of the Prior Art
The present invention relates to a method of treating a waste water containing anionic surfactant and heavy metals such as cadmium, chromium, manganese, mercury, etc. by applying the foam separating process.
The term `foam separating process` herein means a process comprising making a foaming agent such as surfactant be present in a waste water and generating foam by introducing air into the waste water so as to make said foam adsorb the coexisting substances as well as said foaming agent contained in the waste water or to make them adhere to said foam, thereby to separate them from the waste water.
The industrial waste waters discharged from metal refinery works, plating shops, metal processing shops, etc. generally contain not only heavy metals such as Cd, Cr, Mn, Hg, etc. in great quantities, but also anionic surface active agents and other surfactants employed for various washing works. To discharge such waste waters without subjecting them to any purification treatment would lead to the destruction of the environment and cannot be tolerated. At present, therefore, these waste waters containing surfactants and heavy metals are usually treated through the flocculation process and the like, but such conventional methods are still insufficient for attaining a satisfactory result.
In this connection, GRIEVES RB, J, Water Pollution Control Federation 42[8(part)2] R336 - R344(1970) reports a method of removing chromium by applying the foam separating process to a chromium-containing waste water. This method comprises the processes of converting chromium contained in the waste water into the hydroxide thereof and adding a surfactant thereto thereby to perform the foam separation. According to this method, however, the chromium-removing efficiency is insufficient and the loss of treating water is great, so that a fully satisfactory result has not been realized.